Maths!!!

1. If 9 : 2 = 18 : ( z-3 ), find the vale of z.
9/2=18/(z-3)
9(z-3)=2(18)
z-3=4
z=7

2. a : b = 1/2:1/4 , b : c = 1/8 : 1/12 , find a : b : c.
a:b=2:1 and b:c=3:2
Let a=2b and c=2/3b
a : b : c
=2b:b:2/3b
=2:1:2/3
=6:3:2